Casting easily oxidizable metals



Patented July 19, 1932 UNITED STATES PATENT- OFFICE ROBERT THOMAS WOOD, OF LAKEWOOD, OHIO, ASSIGNOB, BY ASSIGNMENTS, IO MAGNESIUM DEVELOPMENT CORPORATION, A CORPORATION OF DELAWARE CASTING EASILY OXIDIZABLE METALS No Drawing.

This invention relates to the casting of the easily oxidizable metals in molds made of sand or similar agglomerated materials. The invention is particularly directed toward processes and meansby which the casting'of these metals may be accomplished without the attendant well known difficulties heretofore encountered. Of the easilyoxidizable metals magnesium is commercially the-most important.

The propensity of metals of the class mentioned to react violently with moisture and to combine with the oxygen and nitrogen of the atmosphere has been a serious obstacle to their successful casting in sand molds.- In accepted foundry practice for ordinary metals there is usually added to the sand or other similar molding materials a tempering medium, in most cases water, which imparts to the sand-the properties necessary to satisfactory molding. It was accordingly supposed that in order to successfully cast mag nesium and similar metals in such molds, the mold must be dried by careful heating in order to prevent attack of moisture on the molten metal.

To overcome the wellknown difficulties, several methods have been suggested. For ex- )ample, it has been propo ed, in conjunction with the drying metho to incorporate in i the molding material a substance which, when the mold becomes heated, will produce a vapor around the metal to protect it from the atmosphere. Obviously the vapor of such a protective substance must have little or no effect on the metal. It has also been proposed to use certain protective substances such as sulfur, urea,.oxalates. or boric acid, which are reported to be usable in an undried sand mold, in the belief that the vapors given off by these substances, when heated, would adequately isolate the metal and protect the same from attack by moisture in the ,mold. Practice, however, has shown that of'these substances sulfur alone exerts a protective action suflicient to permit the use of water as a tempering medium if good castings of commercial size are to be produced.

In spite of the numerous investigations which have been undertaken relative to the Application filed October 23, 1929. Serial No. 401,961.

casting of the easily oxidizable metals in sand molds, the commercial foundry is still faced with difficulties when casting these metals. The drying of the mold is a tedious, expensive process and the incorporation of a protective substance has not been found to produce in all instances the desired effect. As stated above, sulfur may be employed to eliminate the necessity of drying the mold; but in this case also, the castings produced do not represent the optimum in desirable characteristics.

The chief object of the present invention is to provide an improved method of utilizing the protective idea with easily oxidizable metals, to enable sound castings to be obtained, in a commercial foundry, of a good color and free, or substantially so, from oxid films and blow holes. Further objects are to provide a method for the production of sounder and cleaner castings of large size than has heretofore been considered possible; to provide new protective substances and molding mixtures containing the same, by which these methods may be carried out; and to modify and adapt some of the previously known protective substances so as to produce a more efiicient protective efi'ect, particularly in molds containing moisture.

My invention is developed from and pred icated upon an investigation extending over a considerable period of time. In the course of this investigation. in which new and also previously known protective substances were used in both dried and ilndried sand molds and easily oxidizable metals, notably magnesium and its alloys, were cast therein under varied commercial foundry conditions, I observed that while in the presence of some'orotective substances excellent castings might be made, there was a tendency for the cast-. ings to become less satisfactory as their size was increased. Although this had been previously noted, no method has been heretofore developed for satisfactorily overcoming the difficulty.

I have devised a method by which this difficulty may be overcome and good castings of a very considerable size may be produced. I have, moreover, found that this method produces better results with smaller castings than had heretofore, within my knowledge, been obtained. My new method, briefly stated, comprises incorporating in the sand or other molding materials a glycol containing an ethylene IHdICQLPl'CfGIfiblY di-ethylene glycol. The invention also includes the use of one or more other of producing ametal-protecting vapor at successively higher temperatures, preferably such as to produce collectively a substantially continuousemission of protective vapors as the temperature of the mold rises. thus making possible the presence, in the mold and around the casting, of an adequately protective vapor, regardless of the temperature to which the mold is brought by the hot metal.

Most of the methods heretofore devised for casting magnesium or similar metals in sand or the like required that the protective substances be incorporated in the sand and that the mold made from this mixture be thoroughly dried before use in order to eliminate whatever water was added to or was present in the sand. Of the protective substances suggested for use in such dried molds, the polyhydric alcohols and specifically glycerin had been found to be especially efficacious. It had been thought, however, that such polyhydric alcohols were efiicient only when used in dried sand molds. I have found that the contrary is true and that when combined with other protective substances, for example sulfur, ammonium bisulfate, ammonium fluorid, napthalene, and especially boric acid, these alcohols may be used in a moist sand mold with good results- This leads to important advantages, for in the older methods of using the polyhydric alcohols the sand was dried before molding and enough of such alcohols was then added not only to protect the metal but also to lend the proper molding qualities to the sand. By the use of the polyhydric alcohols in aqueous solutions according to my invention, the drying of the sand is rendered unnecessary and the sand is found to have improved molding qualitiesas compared to ones using a non-aqueous solution of polyhydric alcohol as the tempering medium. Moreover, the amount of the alcohol required is materially reduced since it is no longer necessary to add more alcohol than will produce the desired protective effect on the metal. Although glycerin has been mentioned as the desirable polyhydric alcohol for use as a protective substance, I have found that when used in aqueous solutions ethylene glycol and di-ethylenc glycol are markedly superior to glycerin in that substantially the same'efiect is produced by the use of a 25 per cent aqueous solution of either ethylene or di-ethylene glycol as can be produced by the use of a 50 per cent solution of glycerin.

In using aqueous solutions of one of the substances, capable vaporizing temperatures.

expected effect is caused by the presence, in

the sand, of what is probably an organic borate, formed by reaction between the polyhydric alcohol and the boric acid at the elevated temperatures to which the mold is brought by the molten metal. Beilsteins Handbook of Organic Chemistry lists a compound having the formula (C H O,B) which, it is stated, may be obtained by heating glycerin and boric anhydrid together. My experiments indicate that when glycerin and boric acid are present in the sand the compound described by Beilstein, or one much like it, is formed as the mold becomes heated. Possibly the compound produced when ethylene glycol is used has the analogous formula (C H O B) Whatever the actual composition may be, I use the expression organic borate hereinafter to include the compound 7 just referred to and similar compounds, as for example the one listed in Beilstein above and the one formed by reaction between boric acid and di-ethylene glycol. At any rate, by adding to the molding sand a compound formed by the reaction between boric acid and ethylene or (ii-ethylene glycol, which is presumably an ethylene borate or, more generally, an organic borate, I have achieved practically the same results as those obtained with a mixture of boric acid and a polyhydric alcohol. The use of an organic borate alone, or of boric acid and a polyhydric alcohol without other protective substance, gives aprotective effect on magnesium or like metals which is superior to that obtained with any one substance heretofore known to me, and the castings produced are in quality second only to those obtained in molds containing a plurality of protective substances of variant In using boric acid and a polyhydric alcohol (with consequent formation of an organic borate when the metal is poured), I have found that excellent commercial results'can be obtained by incorporating in the molding sand 1 to 3 per cent (by weight) of boric acid and then adding to the mixture enough of a 25 to 75 per cent (preferably about 40 per cent) aqueous solution of ethylene or di-ethylene glycol to Cil I have also found that as a substitute for boric acid ammonium borate may be employed; or borax and a mineral acid, say hydrochloric or sulfuric, which will react with the borax to produce boric acid. These substitutes will give, in combination with the polyhydrie alcohol, substantially the same results as are obtained with boric acid and the same alcohol.

In the further course of my investigations I have found other substances, namely potassium sultid and ammonium bisulfate, which when incorporated in the sand and heated by the molten metal, also exert a protective action suilicient to make possible the production of good castings of the readily oxidizable metals, and they have, moreover, a protective action even in undried molds. These substances, potassium sulfid and ammonium bisulfate, may be used singly; or either may be used with other protective substances in the same mold. Each of them, when present as the only added protective substance, say to the amount of about 2 per cent of the total solids of the mixture, will make possible the production of castings of limited size in undried sand molds. As between them, ammonium bi sulfate is in general preferred. Moreover, either or both of these two substances, the protective properties of which were heretofore unknown, may be used advantageously in practicing my described method of producing large sized castings by means of a plurality of protective agents.

Other substances, some of them already known, may also be used in the above mentioned method. Among these are sulfur, ammonium fluorid, urea, magnesium oxalate. magnesium fluorid, ammonium chlorid, and napthalcne. Many of these substances used singly as the protective substance in dried sand molds do not exert a very eflicient protective effect, and only certain of them have heretofore been supposed capable of exerting a protective action in the presence of moisture. For instance it has been believed heretofore that naphthalene is a successful protective substance only when it is mixed with dried sand, and in one instance at least the use of this compound, in combination with a resin, has been suggested to overcome the difficulties incident to molding when no water is used as a binder. I have found, however, that naphthalene in amounts of 7 to 10 per cent by weight of the total mixture, exerts a protective effect in moist sand which is in some cases adequate, especially for magnesium. I have also discovered that similar hydrocarbons, such as anthracene, chrysenc, etc, produce similar results and I consider them to be substantial equivalents of naphthalene. All of the above mentioned pro-.

tective substances I have used in carrying out my novel method above described. Some are better than others but all, when used boron and organic matter. This is with other substances in accordance with my method, produce an effect superior to that produced by any one of them singly.

In practicing my improved method, by incorporating in the molding material a plurality of substances capable of producing a protective vapor, I have devised certain combinations of protective substances of which examples will now be set forth, and have found that in selecting the various protective substances according to their vaporizing temperatures their boiling points may, in general, be considered to be indicative of their relative vaporizing temperatures. Thus ethylene glycol has a boiling point of 197 (3., naphthalene 218, di-ethylene glycol 250, glycerin 290, sulfur 440, ammonium bisulfate 490. Boric acid volatilizes in steam and in polyhydric alcohols. Ammonium fluorid has no true boiling point but it begins to vaporize and dissociate at comparatively low temperatures. Of ethylene borate it can be said that when the compound is produced by heating ethylene glycol and boric acid in water to simulate the conditions occurring in a sand mold distillates are obtained from about 120 C. to as high as 280 which upon analysis are found to contain probably one reason why ethylene glycol and boric acid are so effective when used together. In some cases I prefer to use an organic borate, for example the ethylene borate just mentioned, as at least one of the plurality of protective substances, and sulfur as another, since I have found that molding mixtures of producing better and larger castings than could heretofore be obtained. However, the presence of both these particular substances is not necessary to produce large sized castings or to produce smaller sized castings of a quality not heretofore obtainable, and in fact in some cases a combination containing only protective substances which were well known before my present invention, produces results superior to any which were theretofore obtained. Among substances usable alone, organic borate, sulfur, naphthalene, and ammonium bisulfate are especially effective, and one or more of these substances are included in each of the mixtures outlined be low, but the invention is by no means limited in that respect. Instead of preparing in advance the organic borate which is formed (I believe) by reaction of the boric acid and ethylene or di-ethylene glycol, for example, it is in general more advantageous to produce the same in situ, so to speak, by incorporating the necessary reagents in the molding mixture. I may also use to advantage ammonium phosphate, the use of which is more fully described in the copending application of Francis C. Frary and myself, Serial No. 401,962, filed concurrently herewith.

manent type. These examples (in which ,the

arts stated are by weight) represent a numr of molding compositions Wh1ch have been found especially advanta eous in casting the easily oxidizable meta s and partic ularly magnesium and itsalloys, according to the precepts of my invention. The water or other tempering medium is added in amount suflicient to give the desired molding consistency.

Examples 1 and 2 l 2 approximately 93 to 97 parts Molding sand Sulfur approximately 6 to 2 parts Boric acid approximately 1 1 part Di-ethylene glycol, 40 per cent aqueous solution Suflicient Sufllcient Example 3 Molding sand approximately 95 parts Sulfur approximately 2 parts Naphthn1ene approximately 3 parts Di-ethylcnc glycol, 40 per cent aqueous solution- Su'fllcient Example I; Molding sand approximately 94 parts Sulfur; approximately 2 parts Anthracene approximately 3 parts Boric acid H approximately 1 part Dl-ethylene glycol, 40 per cent aqueous solution- Sufliclent I Example 5 Molding sand approximately 98 parts P tassium sultid approximately 2 parts Di-ethylene glycol, 40 per cent aqueous solution Sufllcient Example 6 Molding sand approximately 98 parts Borlc acid approximately 2 parts Ethylene glycol, 40 per cent aqueous solution" Snflicient Example 7 Molding sand approximately 95 parts Naphthalene" approximately 4 parts approximately 1 part 40 per cent aqueous solution Sui'licient Example 8 Molding sand approximately 97 parts Ammonium hisulfate approximately 2 parts Borlc acid approximately '1 part Ethylene glycol, 40 per cent aqueous solution Sufllcient Example 9 Molding sand approximately 9 8 parts Ammonium fluorid approximately 2 parts Ethylene glycol, 40 per cent aqueous solution..- Sufljicient Example 10 Molding sand approximately 93 parts Ammonium bisulfate approximately 2 parts Naphthalene approximately 4 parts Bo ir acid approximately 1 part Ethylene glycol, 40 per cent aqueous solution" S'ufllcient Example 11 M lding sand approximately 98 parts Borlc acid approximately 2 parts Ethylene glycol, 25 per cent aqueous -solution Sluflicient Boric acid approximately 1 part Ethylene glycol, 25 per cent aqueous solution Sumcient 1,sos,4os

rate approximately 2 to 8 parts Aqueous solution containing 15 per cent sulfuric acid and 40 per cent ethylene glycol Bufllcient It is to be understood that my invention is not limited to the specific forms herein described but can be carried out in other ways without departure from its spirit. Inventions disclosed but not claimed herein are claimed in my four. copending applications Serial Nos. 401,957, 401,958, 401,959, 401,960, and the aforesaid joint ap lication of Francis C. Frary and myself, erial No. 401,962, all filed of even date herewith.

- I claim- 1. A sand mold tempered with a glycol containing an ethylene radical.

2. A sand mold tempered with di-ethylene glycol.

3. A sand mold tempered with an aqueous solution of di-ethylene glycol.

4. A sand mold tempered with an aqueous solution containing 25 to 75 per cent of diethylene g1 col.

5. A son mold tempered with an aqueous solution of a glycol compound of ethylene.

6. The process of maklng'a casting of magnesium or other easily oxidizable metal, comprising forming a mold from sand rendered moldable by'a tempering medium containing a glycol having an ethylene radical, andv casting said metal in said mold.

7. The process of making a casting of magnesium, comprising forming a mold from sand rendered moldable by a tempering medium containing di-ethylene glycol, and casting said metal in said mold.

8. The method of casting magnesium and other easily oxidizable metals in sand molds, comprising mixing with sand a plurality of protective substances of variant vaporizing temperatures, including a glycol containing an ethylene radical, forming a mold of the mixture, and casting the metal in the mold.

9. The method of casting magnesium and other easily oxidizable metals in sand molds, comprising mixing with sand a plurality of protective substances of variant vaporizing temperatures, including an aqueous solution of a glycol compound of ethylene, forming a mold of the mixture, and casting the metal in the mold.

10. The method of casting magnesium and other easily oxidizable metals in sand molds, comprising mixing with sand a plurality of protective substances of variant vaporizing temperatures including an aqueous solution ctlmtaining 25 to 75 per cent of di-ethylene g yco In testimony whereof I hereto afllx my signature.

ROBERT THOMAS WOOD. 

